Radial lip seal assemblies are used to prevent fluids (liquids or gasses) from leaking around a cylindrical device such as a piston, piston rod, shaft or the like, from a relatively higher pressure region in which the shaft or other cylindrical device is mounted to a relatively lower pressure region. Such radial lip seal assemblies typically include a circular or annular seal body which is sealably fit within a bore formed within a housing surrounding the cylindrical device. An annular-sealing lip extends radially inward from the seal body to form an annular contact around the shaft and provide a slidable sealing surface.
Prior art radial lip seal technology began primarily in the early 1900's. These early lip seals utilized a metallic case that clamped a specially treated piece of leather. The case was sealably attached to the seal housing. The leather was used as a sealing lip and was the wear part of the seal. Elastomer materials soon replaced the leather and greatly enhanced the life and performance of these rotating shaft seals. These elastomer seals were commonly pressed into a seal bore formed in the seal housing. Further developments in seal technology and sealing materials lead to the use of fluoropolymer or fluoroplastic materials for the sealing lip. These fluoroplastic materials offered extended wear life, better chemical compatibility and operability in higher temperature and pressure ranges. In addition, fluoroplastic materials typically do not have a shelf life as compared to the elastomer lip seals. However, radial lip shaft seals made with fluoroplastic materials have several disadvantages. For example, fluoroplastic lip seals can easily cost several times that of similar elastomer lip seals. The added advantages in performance of the fluoroplastic lip seals are thus, sometimes overshadowed by the high seal cost. In addition, fluoroplastic lip seals are susceptible to flow creep, compression set and resizing problems. These problems can lead to premature leakage of the seal.
Presently, the most commonly used rotary lip seals are elastomer "rubber" lip seals. These elastomer lip seals are typically manufactured with a metallic internal member surrounded by an elastomer. The elastomer forms a radially inward extending annular lip and is adapted to make sealing contact against the rotating or reciprocating shaft. Extension springs are commonly used to energize or otherwise maintain the sealing lip in sealable contact against the shaft. These elastomer lip seals can be produced at a relatively low cost compared to most other types of sealing systems. As a result, these elastomer lip seals are widely used throughout the world.
As an alternative to the elastomer type lip seals, fluoroplastic lip seals may be used. As mentioned, these fluoroplastic lip seals typically surpass the performance of the more conventional elastomer lip seal. However, these fluoroplastic lip seals are typically more expensive due to the high cost of the base materials. Fluoroplastic materials are also difficult to bond or mold to the metal components, forcing even higher costs. In addition, the installation of metal cased fluoroplastic seals usually requires a press fit into a seal bore within the seal housing. Special press fit tools may be required to force the seal into the bore. Removal of the seal can be difficult and may score or damage the seal housing bore. Improper handling of the fluoroplastic seal material can lead to leakage across the seal as well as reduced seal life.
When radial lip seals leak or otherwise fail due to wear or damage, they are typically removed and replaced with a new seal. In addition to the cost of the seal itself, seal replacement can be quite expensive and in some applications, economically prohibitive due to the effort required to remove and reinstall the seal. There is thus, a need for a radial lip seal which can be easily replaced or more efficiently repaired and at a more effective cost. In addition, there is a need for a fluoroplastic radial lip seal which is less expensive and is less difficult to install.
It is therefore desirable to provide a radial lip seal having a fluoroplastic sealing element which is simple and economical to both install and remove. In addition, it is desirable that the improved radial lip seal be rebuildable so that the fluoroplastic sealing element may be replaced without the cost of replacing the entire seal. The improved lip seal should have enhanced reliability and longer useful life compared to prior art radial lip seals.